The invention relates to the measurement of the temperature of a particular region, especially (but not exclusively) in a human body for medical purposes, by employing hyperfrequency waves, or microwaves, in the range of 0.5 to 20 GHz.
In practice such a measurement is generally made by means of a microwave radiometer comprising:
a microwave detector (constituted in particular by an antenna or a probe) placed in contact or in immediate proximity to the region, of which it is necessary to measure the temperature and which generates a thermal noise constituted by the emission of microwaves in the aforesaid range of frequencies, said detector emitting a microwave output signal whose intensity is a function of said temperature,
a thermal reference source maintained at a known temperature, possible adjustable, emitting a signal of this known temperature, and
electronic detection and comparison means to deduce, from the output signal of said detector and from the output signal of said source, the temperature of said region.
Such a radiometer is described, for example, in French patent 2.497.947 and U.S. Pat. No. 4,627,442 (to which corresponds the published European patent application 0.114.094).
The most difficult problem posed by the determination of the temperature of a region by means of thermal noise microwaves emitted by this region is that of the calibration, since the signal resulting from the treatment of the microwaves emitted by said region is difficult to connect with the effective temperature of this zone, even when a reference temperature source is employed and a zero method in the comparison of the signals emitted by the region and said source, particularly on account of numerous derivatives resulting from the use of said source.
It is an object of the present invention to resolve this formidable problem of calibration and to permit thus an exact measurement by microwaves of the temperature of a predetermined region.